feat(lsp): Add option to trace LSP communication (#425)

This option is useful to see messages passed between VS and LSP server
to debug issues in LSP server implementations.

Similar functionality is for many other languages, see e.g. previous
changes for go and rust:

golang/vscode-go@70e7c4b
https://github.com/rust-lang/rust-analyzer/pull/302/files

package.json

@@ -193,6 +193,16 @@
                     },
                     "default": [],
                     "description": "The arguments to pass to the LSP executable"
+                },
+                "bazel.trace.server": {
+                    "type": "string",
+                    "enum": [
+                        "off",
+                        "messages",
+                        "verbose"
+                    ],
+                    "default": "off",
+                    "description": "Trace the communication between VS Code and Bazel LSP server (language server)."
                 }
             }
         },

src/extension/extension.ts

@@ -161,7 +161,12 @@ function createLsp(config: vscode.WorkspaceConfiguration) {
     documentSelector: [{ scheme: "file", language: "starlark" }],
   };
 
-  return new LanguageClient("Bazel LSP Client", serverOptions, clientOptions);
+  return new LanguageClient(
+    "bazel",
+    "Bazel LSP Client",
+    serverOptions,
+    clientOptions,
+  );
 }
 
 /**